Seed meters of various designs are used to dispense seeds at a controlled rate into a seed furrow as the seed meter is advanced above and along the seed furrow. In a typical arrangement, a tractor is coupled to tow a tool bar to which are attached in a generally parallel, spaced apart relation, a plurality of planting units each having a seed meter arrangement. Each planting unit typically includes a seed hopper which holds and carries a large quantity of seeds which are to be planted. Alternatively, a smaller container is fed with seeds from a centralized bin or large hopper. The planting unit includes a device for opening a furrow in the ground as the tractor draw tool bar is advanced across the field over the ground. A feed meter is coupled to the seed hopper to dispense individual seeds into the furrow at a controlled rate. The planting unit also typically includes a device for moving soil at the sides of the furrow to close the furrow over the seeds.
During planting, the tractor typically moves across the field at speeds of about 4 to 8 miles per hour. The spacing between adjacent individual seeds in each furrow can be as small as 0.5 inches or less or as much as 10 inches or even more depending upon the particular seed being planted.
The seed metering mechanism therefore, must be capable of dispensing seeds at various rates in the order of 5 to 150 seeds per second. The seed meter mechanism may also be required to dispense seeds at greater rates as well as rates which are less depending on the use.
The types of seeds to be planted using a seed metering mechanism may include, for example, corn, cotton, sorghum, sugar beets, soybeans and sunflowers. As will be appreciated, such seeds vary considerably in size, weight and shape. For example, peanut and edible bean seeds are among the largest seeds for planting and have elongated, irregular shapes and outer surfaces. Soybean and pelletized seeds are smaller and tend to be rounder and vary in shape and size. Sorghum and raw sugar beet seeds have a rounder, almost spherical appearance. Sorghum seeds have a relatively smooth outer surface. On the other hand, raw sugar beet seeds have a very rough and irregular outer surface configuration. Cotton seed is small and shaped like some corn seed. On the other hand, corn seeds have a somewhat triangular shape with generally flat sides.
Despite these numerous differences in size, shape and surface of such seeds, seed meters must handle all different types of seeds described above as well as many more while requiring minimum effort regarding part changes and adjustments. At the same time, required spacing and depth standards of planting accuracy typically mandate a low error rate. A missed seed or doubling of seeds is undesirable and may be tolerated only very infrequently. Such requirements place considerable demand upon the accuracy of the seed metering mechanism.
A significant problem, which must be addressed by such feed metering units, is the ability to easily change from one metering or dispensing speed to another. The speed or rate at which seeds are dispensed has been controlled in existing planters by a sprocket and chain-type transmission. Such transmissions are permanently mounted between individual planting units. The transmission is usually placed in the middle of the planter, between planting units. In such devices, a ground wheel assembly, mounted on a frame, drives the transmission. The transmission in turn rotates a shaft which is connected to the individual planting unit seed meters. This arrangement eliminates the need for a separate drive wheel for each individual unit. Additionally, the rate at which seeds are planted can be adjusted for all of the units by adjusting the single transmission.
In these sprocket and chain-type transmissions, sprockets or sprocket clusters are fixably connected to rotate with a shaft. A chain is entrained between a sprocket on one shaft and a sprocket on another shaft. The rate of seed dispensing is changed by changing the size of one or both of the sprockets around which the chain is entrained.
In one existing system, the sprocket size is changed by physically removing the existing sprocket from the shaft and replacing it with the desired size. This requires a significant amount of effort and time to change the sprocket. Additionally, tools are required to make the change. This system has the obvious disadvantages of requiring a significant amount of effort and time and the need for tools every time the sprocket size is changed.
Another existing system uses sprockets, which are connected to each other in a cluster. The sprocket cluster slides along the length of a shaft but is fixed to rotate with the shaft. A plurality of rubber spacers are arranged on the shaft, on both sides of the sprocket cluster, to hold the sprocket cluster in the desired position. The spacers are split along the axial direction to permit the spacers to be clipped on and off of the shaft. When it is desired to change the size of the sprocket, one or more of the spacers are removed from one side of the sprocket cluster allowing the sprocket cluster to slide along the shaft until the desired sprocket is aligned with the chain. The removed spacers are then mounted on the other side of the sprocket cluster such that the sprocket cluster is held in the desired axial position on the shaft. One problem with this arrangement is that the rubber spaces may fall off of the shaft due to the vibration or movement of the planter in the field. This may be due to the circular inner wall of the spacer, which is engaged with the typically hexagonal shafts. This circular wall has a tendency to help widen the split and force the spacers off the hex shaft. These spacers are also difficult to press on to the hex shaft. Adjustment of this arrangement is therefore cumbersome and time-consuming.
Another concern with existing planter transmissions is their width. Since the transmission is placed between planting units, it is desirable to have a relatively narrow transmission so that the space between adjacent planting units is also narrow.
Therefore, it is an object of the present invention to provide a transmission for a planter with variable feeding rates wherein the adjustment between feeding rates can be adjusted with minimal effort and without the need for special tools.